[Bug tree-optimization/104339] Missing phiopt due to cast

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=104339

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Note after r13-6834-g41ade3399bd1ec, the testcase in comment #0 works as the
cast in the first bb is unused otherwise,
Here is a better testcase:
```
int f(unsigned short y)
{
    unsigned short t =y;
   int tt = y;
   y = -y;
   int yy = y;
   if (t) tt = yy;
   return tt;
}
```